Civil War photographers were most effective at chronicling things that did not move, such as heavy mortars, bridges, tents, and ruins—subjects that cameras had more or less successfully recorded since the medium’s birth twenty years earlier. The essential problem for a war photographer interested in frontline drama was not lack of daring but the long times (two to five seconds depending on the amount of sun) required to properly expose a large-format collodion-on-glass negative typically used in the field. Here, in Petersburg, Virginia, Timothy H. O’Sullivan attempted something extraordinary for the period—an action shot. Whether or not Battery B was truly under fire or just drilling is moot, as the photograph is a welcome exception that offers a lyrical view of the poetics of battlefield artillery.